Rotary pump



Feb. 21, 1928. 1,659,771

C. H. FOX

ROTARY PUMP Filed Feb.20. 1926 2 Sheets-Sheet 1 anveutoz W Gnome Feb. 21, 1928. 1,659,771

C. H. FOX

ROTARY PUMP Filed Feb.20, 1926 2 Sheets-Sheet 2 nveutoz Patented Feb. 21, 1928.

UNITED STATES CHARLES H. FOX, OF CINCINNATI, OHIO.

ROTARY PUMP.

Application filed February 20, 1926. Serial No. 89,581.

This invention relates to improvements in rotary pumps of the type having toothed gears meshin together uid-tight, androtating in a uid-tight casing, and particularly to the structure of the meshing toothed gears or rotors for increasing the efliciency of this type'of pump and obtaining high pumping capacities and delivery pressures to make the same adaptable formotor fire engine service. i t

v The form of tooth of the gears or rotors is an important factor as to the degree of efii ciency, as it is necessary to provide a work ing clearance between the meshing parts and 16 also between the stationary and moving parts, and yet effectively seal the contacts against leakage. Obviously, there are two distinctive pressure zones within the confines of a rotary pump housing, as, pressure 0 upon the intake zone which may either be above or below atmospheric pressure accord ing to the conditions attendant to operation, and second, pressure upon the discharge zone, as developed by the rotors, more usu- 2 ally above atmospheric pressure, but also variable depending upon the conditions attending. Because of the differential pressures, and also b reason of the need for practical working 0 earance-between the stationary and moving surfaces, it is quite impossible to have the actual discharge match the full volumetric displacement of the internal space, as swept by the rotors, when the pump is in action. There is a constant tendency of the fluid which is passed through the pump to transfer itself from a high to a zone of lesser pressure, and the loss incidental to the leakage passage surfaces which are only in more or less intimate contact, is technically known as slip, and it is cus-' tomary to express the loss by slip in terms comparable with the actual displacement as measured by one complete turn of the rotors. r Another difliculty commonly associated with pumps, featuring rotors of the gear or interlocking type, is ineffective sealing of. the interior contacts against leakage due to the failure to provide adequaterelief for such of the fluid passing through the pump as may become entrapped at the point of juncture where the rotors go into mesh, so that undue pressures are developed between the rotors when incompressible fluids are pumped. This is destructive to the pump and also involves unnecessary power losses.

' Therefore, it is'an object of the present invention to provide adequate relief for the escape of incompressible fluids caught between the engaging surface of the rotors, and to force such fluid outwardly preferably from both ends of the rotor "into cavities in the casing, open to the desired discharge zone of the pump, and to appreciably lessen the slip by providing more satisfactory, frictionless, contacts between the surfaces of the rotors when in motion, and the adjacent stationary surfaces of the pump casing or housing.

Another object of the invention is to provide a rotor tooth escapement to the transverse relief passage formed within the .face surface of the tooth, or in providing a split or slitted tooth adapted to communicate with a cavity or recess formed in the casing ad acent on or opposite end surfaces of the tooth and within the discharge zone of the pump.

Other objects and certain advantages of the invention will be more fully set forth in the description of the accompanying drawings forming a part of this specifica tion, in which: 1 j

Figure 1 is a central vertical section through the pump, showing the intake at the lower or base plane, and the discharge at the upper and leading to opposite sides or ends of the pump, although the intake and discharge may be from only one end, the particular arrangement being preferred when the pump is used for fire engine service, as connections can be made from opposite sides or ends.

Figure 2 is a section on line 22, of Fig 1.

igure 3 is a section on line 3-3, of Fig. 1. l I

Referring to the drawings, 1 indicates the body or main casing of the pump of hol- 100 low structure providing a rotor chamber 2 formed by opposite semi-circular walls 3-3 transversely of the casing for an appropriate width of rotor, and head plates 44 respectively fixed to the opposite sides of the body, which serve to seal 'the ends of the pump casing. The chamber 2 at the base thereof is open to communication with an intake passage or conduit 5 within the casing 1. -The passage leads in opposite longilit '77 are mounted within the chamber 2 respectively fixed upon shafts 88 journaled in hearings in the opposite heads 14. The rotor shafts 88 are transmittingly connected by gears 9-9 respectively fixed to the shafts and exterior of the pump casing or one of the heads 4. One of the shafts 8 is provided with a gear -10 in mesh with a gear 11 upon a driving shaft 12 extending through the pump casing and journaled in the heads 4-4. This brings the driving shaft central of the pump and beneath the rotor, a structural advantage when the pump is used for motor fire engine service, the shaftin such instance being coaxial with the transmission shaft of the vehicle motor adapting the vehicle transmission and rotor to be utilized for driving the pump, and therefore, the gear 11 is shown as a sliding gear so that it may be connected and disconnected with the pump gear 10 carried by one of the rotors. r

The crown surface of each tooth of each of the rotors during a portion of its revolution, between the intake and discharge passages of the rotor chamber has a sealing contact with the peripheral wall 3 for conveying the fluids entrapped between two adjacent teeth. The surface of the casin wall 3 swept by the teeth, has a section thereof leading from the intake eccentric to the cir-' cumference of the gear, and a second section thereof leading to the. discharge opening concentric with the said gear circumference.

The end surfaces of the teeth and body of the rotors have a sealing contact with the heads of the pump casing. I

The gear teeth are shown as preferably of the general involute type, and the crown surface preferably of each tooth, i. e., the

tooth periphery, is convexed to constitute a cylindrical surface concentric with the cy lindrical bearing surfaces of the casing walls, respectively, where they are concentric to the respective gear centers, that is, as they move from the intake towards the discharge port. Inasmuch as the roots of the teeth, that is, between individual teeth, conform to the contours of the involute gear tooth type, it follows that there are ample fillets or liquid clearances formed between the crowns of the teeth and the root portions where the teeth are in full intermesh as the gear teeth move away from the discharge port toward flanks of the teeth are contoured to afford intermeshing. contact preventing leakage,

and again the teeth peripheries and root surfaces form a fluid-tight seal when fully intermeshed, appropriately medially of the travel from the discharge to the intake port.

To lessen the slip, and to provide the frictionless contact between these crown surfaces of the gear teeth and the adjacent bearing surfaces of the casing, there is formed in each tooth a cavity 13 for admitting liquid into the body of the tooth as it moves from the eccentric to the concentric casing surface. Preferably this cavity in each tooth, pocket or crevice is in the nature of a split or curf or crevice, extending radially inward toward the gear center from the medial portion of the crown, and this cavity also extends longitudinally or parallel to the axis of the gear from one to the other end of each tooth, thus providing at one or, both ends of the teeth of each gear an aperture or liquid outlet, which of course is sealed by the casing walls as it moves toward the discharge opening, but which in a portion of the travel away from the discharge port moves into communicating relation to a discharge chamber in the casing. The water trap so formed in the gear tooth fills and empties appropriately as the peripheral and end cavity openings are brought into bearing or non-bearing relationship to the casing surfaces, and the endwise draining may be facilitated by inclining the cavity floor in relation to the relief chamber of the casing.

By this construction it will be seen that as the tooth moves in relation to the casing from the inlet to the discharge port, that as the tooth moves past the .eccentric casing surface and closes into valve contact'with the concentric surface the liquid becomes trapped or relieved from pressure and friction by entering these ear tooth cavities. This not only removes ack 7 tion and leaka e, but it constitutes of each tooth holding iquid in its cavity, a liquid seal for the tooth periphery during that portion of the travel toward the discharge port, where both the endapertures and the crown apertures of these cavities are sealed by contact with respective casing surfaces.

As shown in Fig. 1, the lower edge 16 of the relief chamber 14 is in parallelism with the line of common axis ofthe shafts 8-8 and spaced therefrom a distance of slightly more than half the width of the cavity 13,

pressure fricthis edge 16 thus acting to cut off further escape of fluid from the cavity of the meshing tooth as the cavity is aligned with the common axis of the shaft. It is readily apparent that as this position of the cavity in the meshing tooth is reached there is no longer a need for fluid release from the pocket formed by the fillet of the opposite rotor teeth since the pocket is of its smallest dimensions at that point, and is about to be opened to the intake side of the pump.

The base of the cavity is inclined in opposite directions from the width center of rotor downwardly so as to take in approximately the working depth of the tooth. This cavity divides the surfaces of the tooth which contact with the stationary surfaces of the casing wall and heads, and thereby reduces the contacting area of the tooth thereby decreasing the friction, without detriment to the fluid seal established by the contacting surface, and an enhancement to the life of the rotor. The fluid cannot leak or be forced past the surfaces asthe cavity which is closed by the stationary surfaces provides a fluid receiving chamber, to entrap any leakage from the leading edge of the tooth, and conveyed by the tooth into the discharge zone of the pump. Water passing the leading edge of each tooth, causes an eddy in the slot, and the second edge of the tooth acts as a further retardent.

Any leak past the contacting surface de tracts from the efficiency and causes an internal loss, lowering the pump capacity.

Coordinate with the foregoing, thesame means also serves to afford adequate relief for the escape of incompressible fluids and prevent entrapment under increasing pres-.

sure at the meshing or interlocking point of the teeth of the cooperating rotor andthus more effectively sealing the interior contacts against leakage. The entrapment of any incompressed fluid at the point of juncture of the rotors develops pressures between the rotors, results in a percussion which is destructive to the pump and involves power losses. The slot or cavity in each of the teeth of the rotors in advance of and as it reaches the extreme point of juncture with the opposing teeth of the opposite rotor, is at its opposite ends open to respective cavities 13.- 13, one formed in each of the two pump heads, and within the discharge zone ofthe pump. The arrangement, relatively of the split rotor tooth and cavities in the pump heads is such that any fluid collected in between the rotors at the point of intermesh is forced outwardly from both ends of the rotor, into the cavities, and discharge zone of the pump, where the fluid mingles with the common discharge. The fluid cannot become entrapped under undue and increasing pressure' or forced past the sealing or contacting surface of the moving and stationary parts to result. in a leakage acting against the efficiency of the pump.

The tooth slot thus possesses dual advantages to lessen the slip between the surfaces of the rotors when in motion and the adjacent stationary surface and a relief for the escape of incompressible fluids. at the intermesh or points or interior movable contact surface of the rotor, decreasing the power lowering, and leakage.

The shape of the cavit or slot in the teeth may be varied, the design herein disclosed being very simple to machine, and likewise the cavities in the heads may be of various designs or in the singular, that is, in one head only. The slittingis not detrimental to the strength of the tooth.

Having described my invention, I claim:

1. A pump comprising a casing with its intake and discharge ports, a pair of intermeshing liquid-pumping gears operatively positioned in relation to said casing and ports, the said gear teeth being formed with crown surfaces and end faces having fluid tight bearings with portions of the casing, the said crown surfaces of said teeth being formed with.. cavities extending axially through the gear tooth, permitting the en; trance and ejectionof fluid through the gear periphery or ends of the gear teeth, said crown surfaces and pump casing being constituted to form a fluid seal as the gear teeth move from the intake to the discharge port,

and to form also fluid tight seals as the gear teeth move into intermesh approximately midway between the ports, said pump casing being formed with a reliefchamber register-- ing with the end outlets of said cavitiesapproximately at the point of full gear intermesh to drain the cavities endwise into the discharge zone.

2. In combination with a pump casing and. its intake and discharge ports, iutern'ieshing rotary pumping gears operative] y positioned in relation thereto, said casing being formed with a fluid relief chamber leading to the discharge port, the chamber being positioned slightly above the line of common gear-shaft axes in the zone of tooth intermesh, the gear teeth peripheries being formed agd positioned in relation to the casing walls to fiuid seal them in the arc of rotation terminating at the discharge port, the teeth periphery being longitudinally slotted to constitute a tooth fluid-trap open at the gear end adjacent the casing and also open at the peripheral surface of the tooth, sa'd trap being formed for draining fluid en wise into the relief chamber of the casing.

In witness whereof, I hereunto subscribe my name.

CHARLES H. FOX. 

